Tipless transistors, short-tip transistors, and methods and circuits therefor

ABSTRACT

An integrated circuit can include a plurality of first transistors formed in a substrate and having gate lengths of less than one micron and at least one tipless transistor formed in the substrate and having a source-drain path coupled between a circuit node and a first power supply voltage. In addition or alternatively, an integrated circuit can include minimum feature size transistors; a signal driving circuit comprising a first transistor of a first conductivity type having a source-drain path coupled between a first power supply node and an output node, and a second transistor of a second conductivity type having a source-drain path coupled between a second power supply node and the output node, and a gate coupled to a gate of the first transistor, wherein the first or second transistor is a tipless transistor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/533,414 filed Nov. 5, 2014 and entitled “Tipless Transistors,Short-Tip Transistors, and Methods and Circuits Therefor” which is adivisional of 13/708,983 filed Dec. 8, 2012 and entitled “TiplessTransistors, Short-Tip Transistors, and Methods and Circuits Therefor”which claims the benefit of Provisional Application Ser. No. 61/569,038,filed on Dec. 9, 2011, the contents all of which are incorporated byreference herein, in their entirety.

TECHNICAL FIELD

The present invention relates generally to integrated circuit, and moreparticularly to integrated circuits formed with tipless transistors thatdo not include source and/or drain extensions that extend into a channelregion below a control gate and/or that include short-tip transistors.

BACKGROUND

As transistor sizes have decreased, transistor performance has sufferedfrom “short-channel” effects. Some short-channel effects, such asdrain-induced barrier lowering, can arise from depletion regions createdby the source-drain diffusions. Accordingly, at smaller transistorchannel sizes, conventional integrated circuit devices can includetransistors with source and drain extensions (SDEs) that extendlaterally (with respect to the substrate surface) into channel regions,under a gate electrode. Drain and source extensions are typically formedwith “halo” or “tip” ion implantation steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a Deeply Depleted Channel (DDC) transistor.

FIG. 1B is a flow diagram illustrating a general method for forming aDDC transistor.

FIG. 2A shows a tipless DDC transistor according to an embodiment. FIGS.2B and 2C show tipless transistors that can be included in embodiments.FIG. 2D shows a transistor with source-drain extensions (SDEtransistors).

FIGS. 3A and 3B show tipless inverter circuits according to embodiments.

FIGS. 4A to 4C show a tipless pulse generator circuits according toembodiments.

FIG. 5 shows a tipless scannable flip-flop according to an embodiment.

FIG. 6 shows a tipless buffer according to an embodiment.

FIG. 7 shows a tipless “jam” latch according to an embodiment.

FIG. 8 shows a tipless hold buffer according to an embodiment.

FIG. 9 shows a tipless domino logic gate according to an embodiment.

FIG. 10 shows a tipless domino logic gate according to anotherembodiment.

FIG. 11 shows a memory device according to an embodiment.

FIGS. 12A-0 to 12B-1 show transistors that can be included inembodiments.

DETAILED DESCRIPTION

Various embodiments of the present invention will now be described indetail with reference to a number of drawings. The embodiments showintegrated circuits that can include transistors of relatively smallchannel size, while at the same time utilizing “tipless” or “short-tip”transistors for various functions in the integrated circuit device.Tipless transistors can include source and drain vertical dopingprofiles that do not include extension regions that extend in a lateraldirection under a gate electrode. Short-tip transistors can includeextension regions that are shorter than those of other transistors inthe same integrated circuit device.

FIG. 1A shows an embodiment of a deeply depleted channel (DDC)transistor 100 having an enhanced body coefficient, along with theability to set threshold voltage Vt with enhanced precision, accordingto certain described embodiments. The DDC transistor 100 includes a gateelectrode 110, source 112, drain 114, and a gate dielectric 116positioned over a substantially undoped channel 118. Lightly dopedsource and drain extensions (SDE) 120, positioned respectively adjacentto source 112 and drain 114, extend toward each other, setting thetransistor channel length (LG). In the embodiment shown, insulatingspacers 121 can be formed on sides of gate electrode 110.

In FIG. 1A, the DDC transistor 100 is shown as an N-channel transistorhaving a source 112 and drain 114 made of N-type dopant material, formedupon a substrate such as a P-type doped silicon substrate providing aP-well 122 formed on a substrate 124. In addition, the N-channel DDCtransistor in FIG. 1A includes a highly doped screening region 126 madeof P-type dopant material, and a threshold voltage set region 128 madeof P-type dopant material. Screening region 126 can be biased via a bodytap 130. It will be understood that, with appropriate changes to dopantmaterials, a P-channel DDC transistor can be formed.

FIG. 1B is a flow diagram 132 illustrating a general method for forminga DDC transistor having an enhanced body coefficient and reduced a Vt,in accordance with the various embodiments described herein. The processillustrated in FIG. 1B is intended to be general and broad in itsdescription, and more detailed embodiments and examples are set forthbelow. Each block in the flow diagram is illustrated and described infurther detail below, in conjunction with the various alternativesassociated with each block illustrated in FIG. 1B.

In step 134, the process begins at well formation, which can include oneor more different process steps in accordance with differentembodiments. The well formation step 134 includes the steps for formingthe screening region 126, the threshold voltage set region 128 (ifpresent), and the substantially undoped channel 118. As indicated by136, the well formation 134 can be before or after STI (shallow trenchisolation) formation 138.

The well formation 134 can include forming the screening region 126 byimplanting dopants into the P-well 122, followed by an epitaxial (EPI)pre-clean process that is followed by a blanket or selective EPIdeposition. Various alternatives for performing these steps areillustrated in FIG. 1B. In accordance with one embodiment, wellformation 134 can include a beam line implant of Ge/B (N), As (P),followed by an epitaxial (EPI) pre-clean process, and followed by anon-selective blanket EPI deposition, as shown in 134A.

Alternatively, the well formation 134 can include using a plasma implantof B (N), As (P), followed by an EPI pre-clean, then a non-selective(blanket) EPI deposition, as shown in 134B. The well formation 134 canalternatively include a solid-source diffusion of B(N), As(P), followedby an EPI pre-clean, and followed by a non-selective (blanket) EPIdeposition, as shown in 134C. As yet another alternative, well formation134 can also include well implants, followed by in-situ doped selectiveEPI of B (N), P (P) as shown in 134D. As will be described furtherbelow, the well formation can be configured with different types ofdevices in mind, including DDC transistors, legacy transistors, high VTtransistors, low VT transistors, improved ° VT transistors, and standardor legacy aVT transistors. Embodiments described herein allow for anyone of a number of devices configured on a common substrate withdifferent well structures and according to different parameters.

In step 134, Boron (B), Indium (I), or other P-type materials can beused for P-type implants, and arsenic (As), antimony (Sb) or phosphorous(P) and other N-type materials can be used for N-type implants. Incertain embodiments, the screening region 126 can have a dopantconcentration between about 5×10¹⁸ to 1×10²⁰ dopant atoms/cm³, with theselected dopant concentration dependent on the desired threshold voltageas well as other desired transistor characteristics. A germanium (Ge),carbon (C), or other dopant migration resistant layer can beincorporated above the screening region to reduce upward migration ofdopants. The dopant migration resistant layer can be formed by way ofion implantation, in-situ doped epitaxial growth or other process. Incertain embodiments, a dopant migration resistant layer can also beincorporated to reduce downward migration of dopants.

In certain embodiments of the DDC transistor, a threshold voltage setregion 128 is positioned above the screening region 126. The thresholdvoltage set region 128 can be either adjacent to, incorporated within orvertically offset from the screening region. In certain embodiments, thethreshold voltage set region 128 is formed by delta doping, controlledin-situ deposition, or atomic layer deposition. In alternativeembodiments, the threshold voltage set region 126 can be formed by wayof controlled outdiffusion of dopant material from the screening region126 into an undoped epitaxial layer, or by way of a separateimplantation into the substrate following formation of the screeningregion 126, before the undoped epitaxial layer is formed. Setting of thethreshold voltage for the transistor is implemented by suitablyselecting dopant concentration and thickness of the threshold voltageset region 128, as well as maintaining a separation of the thresholdvoltage set region 128 from the gate dielectric 116, leaving asubstantially undoped channel layer directly adjacent to the gatedielectric 116. In certain embodiments, the threshold voltage set region128 can have a dopant concentration between about 1×10¹⁸ dopantatoms/cm³ and about 1×10¹⁹ dopant atoms per cm³. In alternativeembodiments, the threshold voltage set region 128 can have a dopantconcentration that is approximately less than half of the concentrationof dopants in the screening region 126.

In certain embodiments, an over-layer of the channel is formed above thescreening region 126 and threshold voltage set region 128 by way of ablanket or selective EPI deposition (as shown in the alternatives shownin 134A-D), to result in a substantially undoped channel region 118 of athickness tailored to the technical specifications of the device. As ageneral matter, the thickness of the substantially undoped channelregion 118 ranges from approximately 5-25 nm, with the selectedthickness based upon the desired threshold voltage for the transistor.Preferably, a blanket EPI deposition step is performed after forming thescreening region 126, and the threshold voltage setting region 128 isformed by controlled outdiffusion of dopants from the screening region126 into a portion of the blanket EPI layer, as described below. Dopantmigration resistant layers of C, Ge, or the like can be utilized asneeded to prevent dopant migration from the threshold voltage set region128 into the substantially undoped channel region 118, or alternativelyfrom the screening region 126 into the threshold voltage set region 128.

In addition to using dopant migration resistant layers, other techniquescan be used to reduce upward migration of dopants from the screeningregion 126 and the threshold voltage set region 128, including but notlimited to low temperature processing, selection or substitution of lowmigration dopants such as antimony or indium, low temperature or flashannealing to reduce interstitial dopant migration, or any othertechnique to reduce movement of dopant atoms can be used.

As described above, the substantially undoped channel region 118 ispositioned above the threshold voltage set region 128. Preferably, thesubstantially undoped channel region 118 has a dopant concentration lessthan 5×10¹⁷ dopant atoms per cm³ adjacent or near the gate dielectric116. In some embodiments, the substantially undoped channel region 118can have a dopant concentration that is specified to be approximatelyless than one tenth of the dopant concentration in the screening region126. In still other embodiments, depending on the transistorcharacteristics desired, the substantially undoped channel region 118may contain dopants so that the dopant concentration is elevated toabove 5×10¹⁷ dopant atoms per cm³ adjacent or near the gate dielectric116 or by using a very light dose of halo implants. Preferably, thesubstantially undoped channel region 118 remains substantially undopedby avoiding the use of high dosage halo or other channel implants.

Referring still to FIG. 1B, STI formation 138, which, again, can occurbefore or after well formation 134, can include a low temperature trenchsacrificial oxide (TSOX) liner, which is formed at a temperature lowerthan 900° C. as shown by 138A. Embodiments that form the STI structuresafter the blanket EPI deposition step, using a process that remainswithin a low thermal budget, can reduce dopant migration from thepreviously formed screening region 126 and threshold voltage settingregion 128.

As shown in step 140 (FIG. 1B), a gate stack can be formed or otherwiseconstructed above the substantially undoped channel region 118 in anumber of different ways, from different materials, and of differentwork functions. One option is a polysilicon(Poly)/SiON gate stack 140A.Another option is a gate-first process 140B that includesSiON/Metal/Poly and/or SiON/Poly, followed by High-K/Metal Gate. Anotheroption, a gate-last process 140C includes a high-K/metal gate stackwherein the gate stack can either be formed with “Hi-K first-Metal gatelast” flow or and “Hi-K last-Metal gate last” flow. Yet another option,140D is a metal gate that includes a tunable range of work functionsdepending on the device construction. Preferably, the metal gatematerials for n-channel MOS (NMOS) and p-channel MOS (PMOS) are selectedto near mid-gap, to take full advantage of the DDC transistor. However,traditional metal gate work function band-gap settings may also be used.In one scheme, metal gate materials can be switched between NMOS andPMOS pairs as a way to attain the desired work functions for givendevices.

A gate stack may be formed or otherwise constructed above thesubstantially undoped channel region 118 in a number of different ways,from different materials including polysilicon and metals to form whatis known as “high-k metal gate”. The metal gate process flow may be“gate 1st” or “gate last”. Preferably, the metal gate materials for NMOSand PMOS are selected to near mid-gap, to take full advantage of the DDCtransistor. However, traditional metal gate work function band-gapsettings may also be used. In one scheme, metal gate materials can beswitched between NMOS and PMOS pairs as a way to attain the desired workfunctions for given devices. Following formation of the gate stack,source/drain portions may be formed. Typically, the extension portionsare implanted, followed by additional spacer formation and then implantor, alternatively, selective epitaxial deposition of deep source/drainregions.

In step 142, Source/Drain tips can be implanted. The dimensions of thetips can be varied as required, and will depend in part on whether gatespacers (SPCR) are used. In one embodiment, Source/Drain tips are notformed (step 142A), and there may be no tip implant.

In step 144, the source 112 and drain 114 can be formed preferably usingconventional processes and materials such as ion implantation (144A) andin-situ doped epitaxial deposition (144B). Optionally, as shown in step144C, PMOS or NMOS selective EPI layers can be formed in the source anddrain regions as performance enhancers for strained channels. Source 112and drain 114 can further include raised and/or recessed source/drains,asymmetrically doped, counter-doped or crystal structure modifiedsource/drains, or implant doping of source/drain extension regionsaccording to LDD (lightly doped drain) techniques, provided that thethermal budget for any anneal steps be within the boundaries of what isrequired to keep the screening region 126 and threshold voltage settingregion 128 substantially intact.

In step 146, a metal gate is formed in accordance with a gate lastprocess. Step 146 is optional and may be performed only for gate-lastprocesses (146A).

Referring back to FIG. 1A, the channel 118 contacts and extends betweenthe source 112 and the drain 114, and supports movement of mobile chargecarriers between the source and the drain. In operation, when gateelectrode voltage is applied to the DDC transistor 100 at apredetermined level, a depletion region formed in the substantiallyundoped channel 118 can extend to the screening region 126, sincechannel depletion depth is a function of the integrated charge fromdopants in the doped channel lattice, and the substantially undopedchannel 118 has very few dopants. The screening region 126, iffabricated according to specification, effectively pins the depletionregion to define the depletion zone width.

As will also be appreciated, position, concentration, and thickness ofthe screening region 126 can be important factors in the design of theDDC transistor. In certain embodiments, the screening region 126 islocated above the bottom of the source and drain junctions. A screeningregion 126 can be doped to cause a peak dopant concentration to definethe edge of the depletion width when the transistor is turned on. Such adoping of a screening region 126 can include methods such as deltadoping, broad dopant implants, or in-situ doping is preferred, since thescreening region 126 should have a finite thickness to enable thescreening region 126 to adequately screen the well below, while avoidingcreating a path for excessive junction leakage. When transistors areconfigured to have such screening regions, the transistor cansimultaneously have good threshold voltage matching, high outputresistance, low junction leakage, good short channel effects, and stillhave an independently controllable body due to a strong body effect. Inaddition, multiple DDC transistors having different threshold voltagescan be easily implemented by customizing the position, thickness, anddopant concentration of the threshold voltage set region 128 and/or thescreening region 126 while at the same time achieving a reduction in thethreshold voltage variation.

In one embodiment, the screening region is positioned such that the topsurface of the screening region is located approximately at a distanceof Lg/1.5 to Lg/5 below the gate (where Lg is the gate length). In oneembodiment, the threshold voltage set region has a dopant concentrationthat is approximately 1/10 of the screening region dopant concentration.In certain embodiments, the threshold voltage set region is thin so thatthe combination of the threshold voltage set region and the screeningregion is located approximately within a distance of Lg/1.5 to Lg/5below the gate.

Modifying threshold voltage by use of a threshold voltage set region 128positioned above the screening region 126 and below the substantiallyundoped channel 118 is an alternative technique to conventionalthreshold voltage implants for adjusting threshold voltage. Care must betaken to prevent dopant migration into the substantially undoped channel118, and use of low temperature anneals and anti-migration materialssuch as carbon or germanium can be included in embodiments. Moreinformation about the formation of the threshold voltage set region 128and the DDC transistor is found in pending U.S. patent application Ser.No. 12/895,785 filed Sep. 30, 2010, published as U.S. Patent Publication2011/0079861 A1 on Apr. 7, 2011, the entirety of which disclosure isherein incorporated by reference.

Yet another technique for modifying threshold voltage relies onselection of a gate material having a suitable work function. The gateelectrode 110 can be formed from conventional materials, preferablyincluding, but not limited to, metals, metal alloys, metal nitrides andmetal silicides, as well as laminates thereof and composites thereof. Incertain embodiments the gate electrode 110 may also be formed frompolysilicon, including, for example, highly doped polysilicon andpolysilicon-germanium alloy. Metals or metal alloys may include thosecontaining aluminum, titanium, tantalum, or nitrides thereof, includingtitanium containing compounds such as titanium nitride. Formation of thegate electrode 110 can include silicide methods, chemical vapordeposition methods and physical vapor deposition methods, such as, butnot limited to, evaporative methods and sputtering methods. Typically,the gate electrode 110 has an overall thickness from about 1 to about500 nanometers. In certain embodiments, metals having a work functionintermediate between band edge and mid-gap can be selected. As discussedin pending U.S. patent application Ser. No. 12/960,266 filed Dec. 3,2010, issued as U.S. Pat. No. 8,569,128 on Oct. 29, 2013, the entiretyof which disclosure is herein incorporated by reference, such metalgates simplify swapping of PMOS and NMOS gate metals to allow areduction in mask steps and different required metal types for systemson a chip or other die supporting multiple transistor types.

Applied bias to the screening region 126 is yet another technique formodifying threshold voltage of a DDC transistor 100. The screeningregion 126 sets the body effect for the transistor and allows for ahigher body effect than is found in conventional FET technologies. Forexample, a body tap 130 to the screening region 126 of the DDCtransistor can be formed in order to provide further control ofthreshold voltage. The applied bias can be either reverse or forwardbiased, and can result in significant changes to threshold voltage. Biascan be static or dynamic, and can be applied to isolated transistors, orto groups of transistors that share a common well. Biasing can be staticto set threshold voltage at a fixed set point, or dynamic, to adjust tochanges in transistor operating conditions or requirements. Varioussuitable biasing techniques are disclosed in U.S. Pat. No. 8,273,617issued Sep. 25, 2012, the entirety of which disclosure is hereinincorporated by reference.

Advantageously, DDC transistors created in accordance with the foregoingembodiments, structures, and processes, can have a reduced mismatcharising from scattered or random dopant variations as compared toconventional MOS transistors. In certain embodiments, the reducedvariation results from the adoption of structures such as the screeningregion, the optional threshold voltage set region, and the epitaxiallygrown channel region. In certain alternative embodiments, mismatchbetween DDC transistors can be reduced by implanting the screening layeracross multiple DDC transistors before the creation of transistorisolation structures, and forming the channel layer as a blanketepitaxial layer that is grown before the creation of transistorepitaxial structures. In certain embodiments, the screening region has asubstantially uniform concentration of dopants in a lateral plane. TheDDC transistor can be formed using a semiconductor process having athermal budget that allows for a reasonable throughput while managingthe diffusivities of the dopants in the channel. Further examples oftransistor structure and manufacture suitable for use in DDC transistorsare disclosed in U.S. Pat. No. 8,273,617 (previously mentioned above) aswell as U.S. patent application Ser. No. 12/971,884, filed on Dec. 17,2010 and issued as U.S. Pat. No. 8,530,286 on Sep. 10, 2013, and U.S.patent application Ser. No. 12/971,955 filed on Dec. 17, 2010 and issuedas U.S. Pat. No. 8,759,872 on Jun. 24, 2014, the respective contents ofwhich are incorporated by reference herein.

FIG. 1A shows an embodiment of a Deeply Depleted Channel (DDC)transistor 100 that is configured to have an enhanced body coefficient,along with the ability to set threshold voltage Vt with enhancedprecision. A DDC transistor 100 includes a gate electrode 110, source112, drain 114, and a gate dielectric 116 positioned over asubstantially undoped channel 118.

FIG. 2A illustrates a tipless DDC transistor 200 that does not havelightly doped source and drain extensions (SDEs), in accordance with oneembodiment. The tipless DDC transistor 200 is substantially similar tothe DDC transistor 100 (of FIG. 1A) with regard to aspects other thanthe SDEs. The tipless DDC transistor 200 has a weaker drive current(alternatively described as having a weaker drive strength) than a DDCtransistor 100 for a substantially similar drawn gate length, at leastin part because the effective gate length (L_(EFF)) of the DDCtransistor is longer as a result of the absence of the SDEs.

FIG. 2B shows another tipless transistor 200′ that can be included inembodiments. A tipless transistor 200′ can be a non-DDC transistor withsource and drain diffusion profiles (204/206). As shown, while sourceand drains (204/206) may extend under a small portion of a gateelectrode 202, there are no lateral extensions from vertical profiles215 of such regions.

FIG. 2C shows a further tipless transistor 200″ that can be included inembodiments. Again, while source and drains (204/206) may extend under asmall portion of a gate electrode 202, there are no lateral extensionsfrom vertical profiles 215 of such regions.

FIG. 2D shows a transistor 100′ like that of FIGS. 2B and 2C, but withSDEs 132. That is, transistor 100′ of FIG. 2D is not tipless.

It is understood that while FIGS. 1 to 2D are provided to contrasttipless transistors with those that include source/drain extensions,such figures are exemplary. One skilled in the art would understanddiffusion profiles could take various forms.

Various embodiments of circuits described below make reference totipless transistors (NMOS and PMOS). For the embodiments describedbelow, preferably, a tipless transistor is implemented either as atipless-DDC transistor or variant of a DDC transistor, though theembodiments can also be understood in reference to any non-DDC tiplesstransistor (e.g., a legacy or other MOSFET without SDEs). Variousembodiments of circuits described below also make reference to SDEtransistors (NMOS and PMOS). For the embodiments described below, a SDEtransistor can be implemented as either a DDC transistor having SDEs ora non-DDC transistor having SDEs. Similarly, for the embodimentsdescribed below, SDE inverters and SDE logic gates refer to invertersand logic gates that can be implemented using either DDC transistorshaving SDEs or non-DDC transistors having SDEs.

FIG. 3A illustrates a tipless inverter circuit 300 that uses a tiplessNMOS transistor 308-1 and a tipless PMOS transistor 308-0, in accordancewith one embodiment. It is understood that tipless inverter circuit 300can be included in a larger integrated circuit device having othertransistors of smaller sizes, including those having gate lengths ofless than one micron, less than 0.5 micron, or less than 0.25 microns.

In certain embodiments, the tipless NMOS transistor 308-1 can be eithera tipless NMOS DDC transistor or a tipless non-DDC NMOS transistor. Inalternative embodiments, the tipless PMOS transistor 308-0 can be eithera tipless PMOS DDC transistor or a tipless non-DDC PMOS transistor. PMOStransistor 308-0 can have a source-drain path connected between a highpower supply node VDD and output node 309. NMOS transistor 308-1 canhave a source-drain path connected between a low power supply node VSSand output node 309. Gates of transistors (308-0/1) can be commonlyconnected to input node 311. As will be noted in more detail below, insome embodiments, both NMOS and PMOS transistors 308-0/1 can be tiplesstransistors. In other embodiments, one transistor 308-0 or 308-1 can bea tipless transistor while the other 308-1 or 308-0 can be a transistorwith SDE (an SDE transistor).

FIG. 3B illustrates a symbol 305 that is used to represent a tiplessinverter 300 like that of FIG. 3A. The tipless inverter 305 can have alonger rise and/or fall delay time than an inverter formed with SDEtransistors with substantially similar sized transistor. In oneembodiment, a tipless inverter 305 using a tipless NMOS transistor and aSDE PMOS transistor can provide a longer fall delay time than a SDEinverter with NMOS and PMOS transistors of substantially equal drawnsize, while providing a substantially equal rise delay time for the twoinverters. In an alternative embodiment, a tipless inverter using a SDENMOS transistor and a tipless PMOS transistor can provide a longer risedelay time than a SDE inverter with NMOS and PMOS transistors ofsubstantially equal drawn size, while providing a substantially equalfall delay time for the two inverters.

According to embodiments herein, in integrated circuits having smallergeometry transistors, tipless transistors can be used to implement logicgates (e.g., NAND, NOR, etc.), buffers, and inverters, the tiplesstransistors giving rise to an increased delay. In one embodiment, atipless inverter can have the same area (i.e., have transistors of thesame drawn size) as an SDE inverter, but the tipless inverter can havean increased delay. Therefore, if an inverter with increased delay isrequired during optimization of timing paths in an integrated circuit,an SDE inverter can be replaced with a tipless inverter havingtransistors of the same drawn size as the SDE inverter without requiringa layout change or a new place and route step. In one embodiment, theSDE inverter can be replaced with a tipless inverter havingsubstantially identical size and footprint as the SDE inverter byswapping the corresponding cells during a place and route operation.

In alternative embodiments, logic gates using tipless transistors can beused to obtain a desired delay required during timing optimization,where the logic gates using tipless transistors can be substituted forthe logic gates using SDE transistors without requiring a layout changeor a new place and route step.

FIG. 4A illustrates a pulse generator circuit 400 that uses a tiplessinverter 405 as a delay element, in accordance with one embodiment. Apulse generator 400 can include a logic gate circuit 410/415 having oneinput that receives an input signal (CLK_IN) directly, and another inputthat receives the input signal via tipless inverter 405. In the veryparticular embodiment shown, logic gate circuit 410/415 can include aNAND gate 410 and an inverter 415. In one very particular embodiment,NAND gate 410 and inverter 415 can be formed with SDE transistors.

The pulse generator of FIG. 4A is in contrast with a conventional pulsegenerator circuit formed with all SDE transistors (i.e., an SDE pulsegenerator circuit). In a conventional SDE pulse generator circuit, adelay element (corresponding to 405 of FIG. 4A) can be formed with aninverter having long channel SDE transistors, or it can use a delaychain consisting of more than one SDE inverter or long channel SDEinverter.

In one embodiment, a pulse generator circuit using tipless inverters,like those according to embodiments, can be smaller than a SDE pulsewidth generator, because the tipless inverter can require smallertransistor sizes to provide substantially the same delay as the longchannel SDE inverter. In an alternative embodiment, pulse generatorcircuits using delay chains of tipless inverters can have a smaller areathan a SDE pulse width generator using delay chains of SDE invertersbecause a smaller number of tipless inverters can provide asubstantially equivalent delay.

FIG. 4B illustrates waveforms for an operation of the tipless pulsegenerator circuit of FIG. 4A, in accordance with one embodiment. FIG. 4Bincludes the following waveforms: input signal (CLK_IN) and an outputpulse clock (P_CLK_OUT) of the pulse generator 400. The time interval“pulse_delay”, corresponding to the time duration between the risingedge of CLK_IN and the rising edge of P_CLK_OUT, can be determined bythe delay of the NAND gate 410 and the inverter 415. The width of thepulse clock P_CLK_OUT (pulse_width) can be determined by the delay ofthe tipless inverter 405. Typically, the width of the pulse clock(pulse_width) must be sufficiently wide for a pulse latch to sample thedata.

In an alternative embodiment, a tipless inverter 405 can be implementedusing tipless DDC transistors, which can have a reduced σVT (variationin threshold voltage), resulting in reduced variation for the delayprovided by the tipless inverter 405, as well as reduced variation ofthe pulse width. Therefore, the pulse width generator using tipless DDCtransistors can be designed to provide a narrower pulse width (as Vtvariation from non-DDC transistors would provide too much variation inpulse width), which allows a better hold time requirement for a circuit(such as a pulse flip-flop) that is being driven by the pulse clockP_CLK_OUT.

FIG. 4C illustrates an enabled tipless pulse generator 430 that uses atipless inverter 405, in accordance with one embodiment. Enabled pulsegenerator 430 can have a structure like that of FIG. 4A, but with alogic gate 420/425 having three inputs, a third input receiving anenable signal EN. As in the case of FIG. 4A, NAND gate 420 and inverter425 can be implemented with SDE transistors. In the embodiment of FIG.4C, pulses can be generated only when signal EN is active (high in thisembodiment).

FIG. 5 illustrates a scannable flip-flop 500 that uses a tipless holdbuffer 507 as a delay element, in accordance with one embodiment. Thetipless hold buffer 507 can be a buffer implemented using one or moretipless transistors, and can provide the advantages discussed above,such as smaller area, lower capacitance, and lower power dissipation ascompared to a hold buffer implemented using SDE transistors. A delayprovided by the tipless hold buffer 507 can be used to satisfy the holdtime requirement of scannable flip-flops 500 that are connected togetherto form a scan chain, where the output Q of one flip-flop is coupled tothe scan input SI of a next flip-flop (not shown) in the scan chain.

Scannable flip-flop 500 can include an input section formed by transfergates 515-0/1 connected in parallel to input node 523. Transfer gate515-0 can be enabled when signal SE-N is high and SE is low, to passvalue D through to input node 523. Transfer gate 515-1 can be enabledwhen signal SE-N is low and SE is high, to pass value SI through toinput node 523, via tipless hold buffer 507.

Flip-flop 500 can further include clocked latches 517-0/1. Each clockedlatch can include an input transfer gate 525-0/1, a feedback path formedwith an inverter 519 and a clocked inverter 521, and an output inverter527. Input transfer gate 525-0 can be oppositely clocked with respect toinput transfer gate 525-1. In response to clock signals CLK/CLK_N, datavalues can be clocked through latches 517-0/1.

FIG. 6 illustrates a tipless buffer 600 according to one embodiment.Tipless buffer 600 can include a tipless inverter 605 and a SDE inverter610, in accordance with one embodiment. In an alternative embodiment,the inverter 610 can also be implemented as a tipless inverter toprovide a tipless buffer having additional delay.

FIG. 7 illustrates a “jam” latch 700 using a tipless inverter 705, inaccordance with one embodiment. Jam latch 700 can include an inputinverter 729, an input transfer gate 725, a feedback path 731, and anoutput inverter 727. A feedback path 731 can include a tipless inverter705 and a second inverter 733 arranged in series. A tipless inverter 705can maintain the state of the storage node 709 (labeled “DATA_N”) bydriving the storage node DATA_N when it is not being driven by the inputat node DATA, thereby increasing the noise immunity of the jam latch.Data can be written into the jam latch 700 by overpowering or “jamming”the tipless inverter 705 during the write cycle (i.e., forcing thetipless inverter 705 to drive its output in an opposite direction). Ajam latch 700 can operate without a clock controlling the feedback path731, and thus can reduce the clock loading in an integrated circuitusing the jam latch. In addition, the jam latch 700 can dispense withthe generation of complicated control signals to control the operationof the feedback path 731, which can be advantageous, particularly incircuits that can provide more complicated latch functions, e.g., amultiplexing latch.

In one embodiment, the jam latch of FIG. 7 is modified to implement amultiplexing jam latch by replacing the inverter 729, connected betweennodes DATA and DATA_N, with a multiplexer having two or more inputs. Thetipless inverter 705 can be implemented using tipless transistors, andcan provide the advantages discussed above, such as smaller area, lowercapacitance, and lower power dissipation as compared to a feedbackinverter implemented using SDE transistors (e.g., long channeltransistors that are used to provide a feedback inverter with weak drivestrength).

FIG. 8 illustrates a tipless hold buffer 800 in accordance with oneembodiment. Tipless hold buffer 800 can include a number of tiplessinverters (805-0 to -n) arranged in series with one another as delayelements. In the very particular embodiment shown, hold buffer 800 canhave an odd number of tipless inverters (805-0 to -n), followed by a SDEinverter 815 that drives the output node OUT. The SDE inverter 815 canbe implemented using either DDC or non-DDC transistors having SDEs. Thetipless hold buffer 800 can have a smaller size than a hold buffer usingSDE transistors that implement the delay elements using long channeltransistors, since a tipless inverter (805-0 to -n) can providesubstantially the same delay using transistors having a smaller drawnsize than the long channel transistors.

FIG. 9 illustrates a tipless domino logic gate 900 using a PMOS tiplesstransistor 905 as a keeper device, in accordance with one embodiment. Atipless domino logic gate 900 can include a logic input section 950 thatdrives a storage node 909 in response to input signals, a feedback path931, and an output inverter 927. In the very particular embodimentshown, an input section 950 can include a transistor of a firstconductivity type 953 (PMOS in this embodiment) having a source-drainpath connected between a high power supply node VDD and storage node909, and a number of transistors of a second conductivity type (952-0 to-2) (NMOS in this embodiment) having source-drain paths connected inseries between storage node 909 and a second power supply node VSS. Whena clock signal CLK is low, transistor 953 can drive storage node 909high. When clock signal CLK is high, transistor 952-2 can be enabled,and storage node 909 may, or may not, be discharged to VSS throughtransistor 952-2, depending upon logic signals applied to gates oftransistors 952-0/1.

To provide pseudo-static operation, i.e., make the circuit functionalwhen no clock is applied, the tipless transistor 905 functions as afeedback device that supplies current to counteract the leakage currentof the NMOS stack (952-0/1/2). Thus, the leakage current will notdischarge the domino circuit if the storage node 909 should remain high.A drive strength of tipless transistor 901 can be selected to ensurethat tipless transistor 905 is not so strong so as to make the logicgate 900 unwritable, i.e., the NMOS is not strong enough to dischargestorage node 909 when the clock (CLK) is high. This can occur whenprocess variations result in weak NMOS and strong PMOS devices (i.e., aweak NMOS, strong PMOS “corner”).

The tipless domino logic gate 900 is in contrast to a conventional SDEdomino logic gate, which can use a long channel SDE transistor as thekeeper or feedback device. In a conventional SDE domino logic gate thelong channel SDE transistor is typically strong enough to counteract theNMOS stack leakage current while also being weak enough to allow thestorage node 909 to be discharged by the NMOS stack when the clock isactive.

The tipless domino logic gate 900 can be smaller than the SDE dominologic gate because the PMOS tipless transistor 905 can provide a weakfeedback using a smaller drawn transistor size than a comparable longchannel SDE transistor having substantially similar drive strength.

FIG. 10 illustrates a tipless domino logic gate 1000 using a tiplessinverter 1005 as a keeper, in accordance with one embodiment. Tiplessdomino logic gate 1000 can include sections like those of FIG. 9, andsuch like sections have the same reference character, but with theleading digits being 10 instead of 9. FIG. 10 differs from FIG. 9 inthat a feedback path can include an inverter 1033 and tipless inverter1005, with inverter 1033 being connected between a storage node 1009 andan output node OUT.

The tipless inverter 1005 functions as a feedback device that cancounteract the leakage current of the NMOS stack (1052-0/1/2) when theclock is not active, i.e. the clock signal (CLK) voltage is at “0” or“VSS”, so that the leakage current does not change the state of thestorage node 1009 when it is at high or VDD. The tipless inverter 1005can also provide a weak feedback device that allows the storage node1009 to be discharged by the NMOS stack (1052-0/1/2) when the clock isactive and IN_A and IN_B are high.

The tipless domino logic gate 1000 is in contrast with a conventionalSDE domino logic gate, which can use a long channel inverter as thefeedback device, where the long channel inverter is implemented usinglong channel SDE transistors that are weaker than the SDE transistors ina corresponding NMOS stack.

The tipless domino gate 1000 can be smaller than the SDE domino gatebecause the tipless inverter 1005 can provide a weak feedback usingsmaller transistor sizes, as drawn, than the long channel transistors ofa comparable long channel SDE inverter having substantially similardrive strength.

According to embodiments, a tipless inverter, or other tipless delaycircuit as described herein, can be used to advantageously implementprogrammable delay chains in integrated circuit devices. Since a tiplessinverter/delay circuit can have a longer delay than a SDE inverter/delaycircuit using similarly sized transistors, a programmable delay chainusing tipless devices can have fewer stages (e.g., inverters) than aprogrammable delay chain using SDE inverters to provide a predetermineddelay. The programmable delay chain using tipless transistors can have alower capacitance as a result of having fewer inverters, and therefore,it can have lower power dissipation than a programmable delay chain withSDE inverters. The programmable delay chain using tipless inverters canalso have a smaller area since it can provide the predetermined delayusing fewer inverter stages. In alternative embodiments, the area,delay, power dissipation, and leakage of the programmable delay chaincan be adjusted to have a predetermined value that is determined by theselection of the source/drain extension tip length for the transistorsused in the programmable delay chain.

Programmable delay chains according to embodiments can be included invarious integrated circuit devices. One such embodiment is shown in FIG.11.

FIG. 11 illustrates an integrated circuit memory device 1100 accordingto an embodiment. A memory device 1100 can include a memory array 1161,decoder circuits 1163, sense amplifier circuits 1165, a datainput/output (I/O) section 1167, an address latch 1169, and a timing andcontrol circuit 1171. A memory array 1161 can include memory cells forstoring data, including but not limited to: dynamic random access memory(DRAM) cells, static RAM (SRAM) cells, and/or nonvolatile memory cells.Decoder circuits 1163 can decode addresses to access memory cells. I/Osection 1167 can provide data read and write (program) paths for memorycell array. Address latch 1169 can store received address values (ADD).Control circuit 1171 can generate timing and control signals based onreceived control data, and in the particular embodiment shown, a clocksignal CLK.

Sense amplifier circuits 1165 can amplify signals from memory cells togenerate read data values for output from the memory device 1100. In theembodiment shown, sense amplifier circuits 1165 can be activated inresponse to a sense amplifier enable signal (saen). In high performancememory devices, the timing of a saen signal can be adjusted to optimizeperformance.

In the embodiment shown, control circuit 1171 can generate a senseamplifier signal (sa) in response to timing signals and read controlsignals (e.g., read commands). A sense amplifier signal (sa) can bedelayed by a tipless programmable delay chain 1180, to generate the saensignal. A tipless programmable delay chain 1180 can take the form of anyof those shown herein, or equivalents. A tipless programmable delaychain 1180 can provide a desired delay with a smaller size, lower powerconsumption, and fewer stages than a conventional SDE delay circuit.

According to embodiments, a tipless inverter or other tipless delaycircuit can also be used as delay elements in a clock modification orgeneration circuit, such as a delay locked loop (DLL) or phase lockedloop (PLL). As in the case of tipless programmable delay chains, theinclusion of tipless delay circuits in DLL or PLL like circuits canallow for fewer delay stages, for lower power dissipation, as well assmaller area. Tipless DLL/PLL type circuits according to embodiments canbe included in various integrated circuit devices. One such embodimentis shown in FIG. 11.

Referring once again to FIG. 11, a memory device 1100 can include acontrol circuit 1171 to generate timing and control signals. In theembodiment shown, control circuit 1171 can include a PLL and/or DLL 1173for generating timing signals having a desired phase or frequency shiftwith respect to another clock signal (i.e., CLK). The PLL/DLL circuit1173 can include tipless delay elements 1105, in the form of tiplesstransistors, inverters, pulse generators, etc.

While embodiments above have shown the inclusion of tipless transistorsin integrated circuit devices, alternate embodiments can utilize“short-tip” transistors in addition to, or as a substitute for, tiplesstransistors.

Accordingly, alternate embodiments can include any of the circuitsdescribed with reference to FIGS. 3A-11, where any or all tiplesstransistors/circuits are substituted with short-tip transistors. Forthese alternative circuit embodiments, a short-tip transistor can beimplemented either as a DDC or a non-DDC transistor with shorter SDEsthan a conventional SDE transistor. The short-tip transistor can have anintermediate drive strength that is weaker than a SDE transistor andstronger than a tipless transistor, where each of the transistors hassubstantially similar drawn size. In other embodiments, the length ofthe SDEs for the short-tip transistors can be selected to obtain apredetermined delay required for the circuits described above. Forexample, the SDE lengths of the short-tip transistors in the short-tipinverter can be selected to provide predetermined rise and fall delaytimes without modifying the drawn sizes of the short-tip transistors.Therefore, if an inverter with a predetermined delay is required duringoptimization of timing paths in an integrated circuit, an SDE invertercan be replaced with a short-tip inverter having transistors withappropriately selected SDE lengths without requiring a layout change ora new place and route step, where both inverters have transistors withsubstantially similar drawn sizes.

FIG. 12A-0 illustrates a conventional SDE transistor 1200A formed in asubstrate 1214, having a gate electrode 1202, gate insulator 1228,source 1204, drain 1206, and SDEs 1232.

FIG. 12A-1 illustrates a short-tip transistor 1201A formed in asubstrate 1214, having a gate electrode 1202, gate insulator 1228,source 1204, drain 1206, and short-tip SDEs 1280. Short tip SDEs 1280can extend to a lesser extent in a lateral direction than conventionalSDEs 1232 in FIG. 12A-0.

FIG. 12B-0 illustrates a DDC transistor 1200B formed in a substrate1214, having a gate electrode 1202, gate insulator 1228, source 1204,drain 1206, and SDEs 1232.

FIG. 12B-1 illustrates a short-tip DDC transistor 1201B formed in asubstrate 1214, having a gate electrode 1202, gate insulator 1228,source 1204, drain 1206, and short-tip SDEs 1280. Short tip SDEs 1280can extend to a lesser extent in the lateral direction than conventionalSDEs 1232 in FIG. 12A-0.

It should be appreciated that in the foregoing description of exemplaryembodiments of the invention, various features of the invention aresometimes grouped together in a single embodiment, figure, ordescription thereof for the purpose of streamlining the disclosureaiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the detailed description are hereby expressly incorporatedinto this detailed description, with each claim standing on its own as aseparate embodiment of this invention.

It is also understood that the embodiments of the invention may bepracticed in the absence of an element and/or step not specificallydisclosed. That is, an inventive feature of the invention may beelimination of an element.

Accordingly, while the various aspects of the particular embodiments setforth herein have been described in detail, the present invention couldbe subject to various changes, substitutions, and alterations withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. An integrated circuit, comprising: a first deeplydepleted channel transistor formed in the substrate and having a firstsource-drain current path coupled between a first and a second node, thefirst deeply depleted channel transistor having a first source drainvertical doping profile with a first extension region that extends in alateral direction under a gate electrode of the first deeply depletedchannel transistor, the first deeply depleted channel transistor beingconfigured to selectively couple a first output node to the first orsecond node in response to one or more input signals, the first deeplydepleted channel transistor having a first drawn gate length of lessthan one micron; and a second deeply depleted channel transistor formedin the substrate and having a second source-drain current path coupledbetween the first node and the second node, the second deeply depletedchannel transistor having a second source drain vertical doping profilewith a second extension region of which dopant concentration is lessthan dopant concentration of the first extension region, the seconddeeply depleted channel transistor being configured to selectivelycouple a second output node to the first or second node in response tothe one or more input signals, the second deeply depleted channeltransistor having a second drawn gate length of less than one micron andsame channel doping profile as a channel doping profile of the firstdeeply depleted channel transistor.
 2. The integrated circuit of claim1, wherein: the first deeply depleted channel transistor having a firstsource and drain having the first source drain vertical doping profiledoped to a first conductivity type, a first substantially undopedchannel region, and a first highly doped screening region of the secondconductivity type formed below the first substantially undoped channelregion.
 3. The integrated circuit of claim 1, wherein: the second deeplydepleted channel transistor having a second source and drain having thesecond source drain vertical doping profile doped to a firstconductivity type, a second substantially undoped channel region, and asecond highly doped screening region of the second conductivity typeformed below the second substantially undoped channel region.
 4. Theintegrated circuit of claim 1, further including: a delay circuitconfigured to delay an electrical signal and comprising at least thesecond deeply depleted channel transistor.
 5. The integrated circuit ofclaim 4, further including: a logic gate configured to logically combinesignals at a plurality of gate inputs to generate a gate output signal;and the delay circuit is coupled to a first gate input of the logicgate.
 6. The integrated circuit of claim 5, further including: a pulsegenerator that includes the logic gate having a second gate inputcoupled to receive an input signal, and the delay circuit is coupled toreceive the input signal and has a delay circuit output coupled to thefirst gate input.
 7. The integrated circuit of claim 6, wherein: thepulse generator further includes the logic gate having a third gatecoupled to receive an enable signal that enables and disables the pulsegenerator circuit.
 8. The integrated circuit of claim 6, furtherincluding: a flip-flop circuit comprising a plurality of latchesarranged in series, each latch having a clocked input, passgates coupledin parallel to an input of the flip-flop circuit, and the delay circuitis coupled to an input of one of the passgates.
 9. The integratedcircuit of claim 6, further including: a memory cell array; senseamplifier circuits coupled to the memory cell array and configured tosense data values from memory cells of the memory cell array, the senseamplifier circuits being enabled in response to a sense amplifiercontrol signal; a control circuit configured to generate an initialsense amplifier control signal; and the delay circuit is configured todelay the initial sense amplifier control signal to generate the senseamplifier control signal.
 10. The integrated circuit of claim 5, furtherincluding: a timing control circuit configured to generate a periodictiming clock for the integrated circuit, and comprising the delaycircuit; wherein the timing control circuit is selected from the groupof: a phase locked loop circuit and a delay locked loop circuit.
 11. Theintegrated circuit of claim 1, wherein: the first deeply depletedchannel transistor has the first drawn gate length of less than 0.5micron; and the second deeply depleted channel transistor has the seconddrawn gate length of less than 0.5 micron.